GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2008 🢒 Unit Repair 🢒 Engine 🢒 Engine Controls and Fuel - LS Engines 🢒 DTC P0685, P0689, or P0690

Diagnostic Instructions
    • Perform the Powertrain On Board Diagnostic (OBD) System Check prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0685: Engine Controls Ignition Relay Control Circuit

DTC P0689: Engine Controls Relay Feedback Circuit Low Voltage

DTC P0690: Engine Controls Relay Feedback Circuit High Voltage

Circuit/System Description

The Powertrain Relay is controlled by the engine control module (ECM). Battery positive voltage is supplied to the relay coil and switch. When the ignition switch is turned to the ON position, the ECM will provide ground on the control circuit of the relay using a low side driver. This will allow voltage through the relay switch contacts to the components. The ECM monitors the voltage level on the control circuit of the relay and the ignition 1 voltage circuit.

Conditions for Running the DTC

P0685

    • The ignition is ON, or the engine is operating
    • The ignition voltage is between 9-16 volts
    • The DTC runs continuously once the above conditions are met

P0689

    • DTC P0685 is not set
    • The ignition is ON, or the engine is operating
    • The powertrain relay is commanded ON
    • The DTC runs continuously once the above conditions are met

P0689

    • DTC P0685 is not set
    • The DTC runs continuously once the above conditions are met

Conditions for Setting the DTC

P0685

The ECM detects the powertrain relay control circuit is open, shorted to ground, or shorted to voltage open for greater than 5 seconds.

P0689

The ECM detects the powertrain relay switch circuit is open for greater than 5 seconds.

P0690

    • The ECM detects greater than 16 volts on the powertrain relay switch circuit when the relay is commanded ON.
        OR
    • The ECM detects greater than 2 volts on the powertrain relay switch circuit when the relay is commanded OFF.
    • The condition exists for greater than 2 seconds.

Action Taken When the DTC Sets

DTCs P0685, P0689, and P0690 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0685, P0689, and P0690 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Engine Control Module Scan Tool Information

Circuit/System Verification

Important: If you were sent here from Engine Cranks But Does Not Run proceed to Circuit/System Testing.

  1. Ignition ON, observe the DTC information with a scan tool. DTCs P0685, P0689, or P0690 should not set.
  2. Cycle the ignition from OFF to ON. You should hear and feel an audible click from the powertrain relay. Repeat as necessary in order to verify powertrain relay operation.
  3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
  1. Ignition OFF, disconnect the powertrain relay.
  2. Ignition ON, verify a test lamp illuminates between the relay coil ignition circuit terminal 85 and ground.
    3. ⇒If the test lamp does not illuminate, repair the relay coil ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect a test lamp between the relay coil control circuit terminal 86 and the relay coil ignition circuit terminal 85.
    4. ⇒If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.
  4. Ignition ON, the test lamp should illuminate.
    5. ⇒If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  5. Connect a 15A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay switch ignition 1 voltage circuit terminal 87.
  6. Attempt to start the engine. The engine should start.
    7. ⇒If the engine does not start, test the relay switch ignition 1 voltage circuit between the EC ignition relay and the ECM for a short to ground or for an open/high resistance. If the circuit tests normal, replace the ECM.
  7. If all circuits test normal, test or replace the powertrain relay.

Component Testing
  1. Ignition OFF, disconnect the powertrain relay.
  2. Test for 70-110 ohms between terminals 85 and 86.
    3. ⇒If not within the specified range, replace the powertrain relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If not the specified value, replace the relay.
  4. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.
    5. ⇒If greater than the specified range, replace the powertrain relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Engine Control Module Replacement for ECM replacement, setup, and programming